Implant placement

ABSTRACT

Embodiments of the present invention relate generally to implant placement into bone. More specifically, embodiments of the invention relate to implant placement across the sacro-iliac joint. Placement can be facilitated using various CT imaging views that allow the implants to be placed in bone associated with articular cartilage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/891,326, filed Oct. 15, 2013, and titled “IMPLANT PLACEMENT,”which is herein incorporated by reference in its entirety for allpurposes.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

FIELD

Embodiments of the invention relate generally to implant placement intobone. More specifically, embodiments of the invention relate to implantplacement across the sacro-iliac joint.

BACKGROUND

Many types of hardware are available both for the fixation of bones thatare fractured and for the fixation of bones that are to be fused(arthrodesed).

For example, the human pelvic girdle (see FIGS. 1 and 2) is made up ofthree large bones joined together by three relatively immobile joints.One of the bones is called the sacrum and it lies at the bottom of thelumbar spine, where it connects with the L5 vertebra. The other twobones are commonly called “pelvic bones” and are technically referred toas the right ilium and—the left ilium. The sacrum connects with bothpelvic bones at the sacroiliac joint (in shorthand, the SI-Joint).

The SI-Joint functions to transfer forces from the spine to the lowerextremities, and vice-versa. The SI-Joint has been identified as thepain generator in up to 22% of patients who present with lower backpain.

Sacroiliac joint fusion is a surgical procedure that is performed toalleviate pain coming from the SI joint in patients who have failed toreceive adequate pain relief with non-surgical treatments of the SIjoint. Some conditions of the SI joint that may be treated with SI jointfusion (arthrodesis) are: degenerative sacroiliitis, inflammatorysacroiliitis, iatrogenic instability of the sacroiliac joint, osteitiscondensans ilii, or traumatic fracture dislocation of the pelvis.Currently, screws and screws with plates are used as the standardinstrumentation for sacro-iliac fusion. Historically, an SI joint fusionconsisted of an open surgical approach to the SI joint from an anterior,a posterior, or a lateral direction. The surgeon would then debride(remove) the cartilage from the articular portion of the joint and theinterosseous ligament from the fibrous portion of the joint. These openapproaches require a large incision and deep soft tissue dissection toapproach the damaged, subluxed, dislocated, fractured, or degenerativeSI joint.

A typical technique for placing implants involves placement of one ormultiple implants from a lateral to medial direction across theSI-Joint. These implants are placed with a starting point on the lateralaspect of the ilium. The implants are then directed across the ilium,across the sacroiliac joint and into the sacrum. Regarding implantposition, care is taken to avoid impinging on neural and vascularstructures, including neural tissue within the neural foraminae orspinal canal. In addition, care must be taken to place the implantsacross the SI joint and avoid the leading tip(s) of the implant(s)violating the osseous envelope of the sacrum. However, the density ofthe bone in different portions of the sacrum is not typically aconsideration during implant placement.

Accordingly, it would be desirable to provide systems and methods forplacing multiple implants across the SI-Joint into those portions of thesacrum with relatively higher bone density. Implants placed into denser(stronger) bone will demonstrate improved short-term and long-termmechanical stability of the implant construct spanning the SI-Joint postimplantation.

SUMMARY OF THE DISCLOSURE

The present invention relates generally to implant placement into bone.More specifically, embodiments of the invention relate to implantplacement across the sacro-iliac joint.

In some embodiments, a method of implanting a plurality of implants inthe SI-joint is provided. The method can include inserting a pluralityof guide pins into an anterior portion of the SI-joint that isassociated with articular cartilage; creating a bore around each of theplurality of guide pins; and inserting an implant into each bore suchthat each implant is located in an anterior portion of the SI-joint thatis associated with articular cartilage.

In some embodiments, the method further includes obtaining a lateralview of the pelvis; and identifying a plurality of anatomical landmarksin the lateral view including the alar line, the posterior sacral bodyline, the anterior sacral body line, and the anterior cortex of thesacral alar, wherein the plurality of guide pins are inserted withreference to at least one anatomical landmark.

In some embodiments, at least one guide pin and implant are insertedanterior of the anterior sacral body line in the lateral view.

In some embodiments, at least two guide pins and implants are insertedanterior of the anterior sacral body line in the lateral view.

In some embodiments, the at least one guide pin and implant that isinserted anterior of the anterior sacral body line in the lateral viewis angled with respect to the horizontal axis in the inlet view.

In some embodiments, at least two guide pins and two implants are placedparallel to the alar line.

In some embodiments, the plurality of guide pins are parallel in theoutlet view.

In some embodiments, the method further includes identifying a targetfor the plurality of guide pins in the inlet view, wherein the target islocated in the middle of the sacral body.

In some embodiments, the method further includes advancing the guidepins towards the target in the inlet view.

In some embodiments, the implants are non-colinear in the lateral view.

In some embodiments, the implants have an elongate body with alongitudinal axis and a rectilinear cross-sectional profile transverseto the longitudinal axis.

In some embodiments, the implants are screws.

In some embodiments, a system for fixation of the SI-joint is provided.The system can include a first elongate implant that is inserted intothe SI-joint through a cephalad portion of the articular cartilage inthe SI-joint; a second elongate implant that is inserted into theSI-joint through a middle portion of the articular cartilage in theSI-joint, wherein the second elongate implant is caudal and anterior tothe first elongate implant; and a third elongate implant that isinserted into the SI-joint through a caudal portion of the articularcartilage in the SI-joint, wherein the third elongate implant in caudalto the second elongate implant.

In some embodiments, the first elongate implant is inserted into theSI-joint caudal to the alar line and between the posterior sacral bodyline and the anterior sacral body line in a lateral view.

In some embodiments, the second elongate implant is inserted into theSI-joint caudal to the alar line and anterior to the anterior sacralbody line in a lateral view.

In some embodiments, the third elongate implant is inserted into theSI-joint anterior to the anterior sacral body line in a lateral view.

In some embodiments, the first elongate implant is positionedhorizontally in an inlet view and the second elongate implant is angledwith respect to the first elongate implant in the inlet view.

In some embodiments, the first elongate implant, the second elongateimplant, and the third elongate implant each have an elongate body witha longitudinal axis and a rectilinear cross-sectional profile transverseto the longitudinal axis.

In some embodiments, the first elongate implant, the second elongateimplant, and the third elongate implant each are screws.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe claims that follow. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIGS. 1 and 2 illustrate anterior and posterior views of the pelvicgirdle.

FIG. 3 illustrates the position of a patient on a Jackson table for CTimaging of the pelvic girdle.

FIGS. 4A-4C are three imaging views of the pelvis, a lateral view of thesacrum shown in FIG. 4A, an inlet view of the pelvis shown in FIG. 4B,and an outlet view of the pelvis shown in FIG. 4C.

FIG. 5 illustrates an annotated lateral radiographic view of the lowerlumbar spine and sacrum that shows various anatomical landmarks.

FIGS. 6A and 6B illustrate landmarks in the lateral view that can beused to position and orient the C-arm to obtain a true lateral view.

FIGS. 7A and 7B illustrate locations on the patient's skin that may bemarked to provide visual guidance or mapping that correlates with theposition of various osseous landmarks identified using the lateralradiographic view.

FIGS. 8A and 8B illustrate how the skin marks in FIGS. 7A and 7B may beused as a guide to align the C-arm in the outlet view and the inletview.

FIGS. 9A and 9B illustrate anatomical features and landmarks of theoutlet view and the inlet view, respectively.

FIGS. 9C and 9D illustrate a lateral view and an inlet view that showsthat the anterior cortex of the sacral ala is visible as the mostanterior aspects of the sacrum.

FIGS. 10A and 10B are lateral views that illustrate an embodiment of animplant target zone that results in the implants passing through thearticular or hyaline cartilage portion of the SI-joint rather than thefibro cartilaginous portion of the SI-joint.

FIG. 10C illustrates a first implantation site placed with reference toboth the alar line and the posterior sacral body line.

FIG. 10D illustrates a second implantation site that can be placed withreference to the alar line and the location of the first implantationsite such that the second implantation site is inferior (caudal) andanterior to the first implantation site and placed in a middle portionof articular cartilage, near the vertex of the boomerang.

FIG. 10E illustrates a third implantation site that can be placed withreference to the anterior sacral body line and the second implantationsite, so that the third implantation site is positioned in an inferior(caudal) portion of the articular cartilage.

FIGS. 11A-11C illustrate the orientation of a first guide pin insertedinto the first implantation site in the lateral view, the inlet view,and the outlet view.

FIGS. 12A-12C illustrate the orientation of a second guide pin insertedinto the second implantation site in the lateral view, the inlet view,and the outlet view.

FIGS. 13A-13C illustrate the orientation of a third guide pin insertedinto the third implantation site in the lateral view, the inlet view,and the outlet view.

FIGS. 14A-14C illustrate the orientation of the three guide pins in thelateral view, the inlet view, and the outlet view.

FIGS. 15A-15C illustrate another embodiment of the third guide pinposition and orientation when the third implantation site is located inbetween the posterior sacral body line and the anterior sacral body linein the inlet view.

FIGS. 16A and 16B illustrate an assembly for receiving the guide pin.

FIG. 17 illustrates a pin depth gage for determining the depth ofinsertion of the pin.

FIG. 18 illustrates removal of a pin sleeve from the guide pin.

FIG. 19 illustrates insertion of a drill over the guide pin.

FIG. 20 illustrates drilling a bore through the lateral cortex of thesacrum in the outlet view.

FIG. 21 illustrates removal of the drill after drilling the bore.

FIG. 22A-22C illustrate alignment of a soft tissue protector withreference to anatomical landmarks so that the faces of the rectilinearimplant are properly oriented with respect to the anatomical landmarks.

FIG. 23 illustrates shaping the bore with a broach.

FIG. 24 illustrates broach advancement across the SI-joint.

FIGS. 25A and 25B illustrate implant insertion over the guide pin.

FIG. 26 illustrates implant advancement.

FIGS. 27A and 27B illustrates implant advancement under CT imaging.

FIG. 28 illustrates implant placement under CT imaging.

FIGS. 29A and 29B illustrate various types of implants that can beimplanted across the SI-joint using the procedures described herein.

DETAILED DESCRIPTION

Pre-Op Preparation and Patient Setup

A computed tomography (CT) scan may be taken of the pelvis and SI-Jointsprior to surgery to check for anatomic anomalies and to identify osseouslandmarks useful for implant placement. The patient may be placed on aflat radiolucent table, such as a Jackson table, to facilitateintra-operative imaging. Although one C-arm is typically employed, somesurgeons may employ two C-arms, with one C-arm set in the lateralposition and the other C-arm rotatable between the inlet and outletpositions, as further described below. As illustrated in FIG. 3, thepatient may be placed on a flat Jackson type imaging table 300 withtowel rolls 302 or other support structures placed transversely underthe patient's chest and waist. This position allows the abdomen to hangfree resulting in diminished intraabdominal pressure. Pillows 304 orother support structures can be placed under the patient's feet to relaxthe knees. After the patient has been properly positioned, a lateralview, an inlet view, and an outlet view may be taken of the SI-Joint andpelvis. The surgeon may identify any abnormalities that could interferewith the procedure and may also confirm that the anatomical landmarksused to guide implant placement are visible.

Intraoperative Imaging

As illustrated in FIGS. 4A-4C, three imaging views, a lateral view ofthe sacrum shown in FIG. 4A, an inlet view of the pelvis shown in FIG.4B, and an outlet view of the pelvis shown in FIG. 4C, may be used tofacilitate safe insertion and placement of instruments, tools andimplants during the procedure. These fluoroscopic views allow thesurgeon to identify various anatomical structures and landmarks, whichmay be used to assist the surgeon in placing the implants into a safeand biomechanically advantageous position. These intra-operativeradiographic views may also be acquired using intra-operative CT scansand/or x-ray imaging.

FIG. 5 illustrates an annotated lateral radiographic view of the lowerlumbar spine and sacrum. Various landmarks that may be used tofacilitate implant placement are notated on this image. In the lateralview, the sacrum will appear as a curved wedge, with the posteriorsacral cortical wall and the anterior sacral cortical wall being readilyvisible. In standard radiographic views denser tissues such as bonegenerally show up as white or light grey and the less dense soft tissuesgenerally show up as black or dark grey. The posterior sacral corticalwall and the anterior sacral cortical wall appear as slightly curveddense white lines that define a triangular wedge shape on the lateralview. Other osseous anatomic landmarks useful for orientation andpositioning include the sacral ala, the pelvic brim, the greater sciaticnotch, the superior endplate of the S1 vertebrae and the inferiorendplate of the L5 vertebrae.

The C-arm may be positioned to allow a true orthogonal lateral view ofthe sacrum and lower lumbar spine. FIGS. 6A and 6B illustrate landmarksin the lateral view that can be used to position and orient the C-arm toobtain this true lateral view. An initial lateral fluoroscopic image isobtained and then the C-arm positioning is adjusted until certainanatomic landmarks (left and right) are superimposed on the lateralimage signaling that the C-arm is aligned correctly. For example, thedisk space between the endplates of L5 and S1 may be aligned based onthe initial lateral fluoroscopic imaging and subsequent adjusted imagesuntil the visualized endplates of L5 and S1 are parallel and in focus,which occurs when the disk space is perpendicular to the image plane. Atthis point the two sciatic notches, one from the right ilium and onefrom the left ilium, should overlap on the lateral fluoroscopic images.The alignment is considered final when the left and right iliac corticaldensities, which are also known as the alar lines, are directlysuperimposed on the lateral fluoroscopic image. The C-arm and the tableare adjusted in multiple planes until the alignment described above isachieved.

As illustrated in FIGS. 7A and 7B, once a true lateral view has beenobtained, the patient's skin may be marked to provide visual guidance ormapping on the patient's skin that correlates with the position ofvarious osseous landmarks identified using the lateral radiographicview. For example, the skin may be marked along the sacral ala andpelvic brim to create a first mark 700, and the skin along the posteriorcortex of the sacral body can be marked to create a second mark 702, asillustrated in FIGS. 7A and 7B. In addition, a third mark 704 may beplaced overlying the anterior cortex of the sacral body. One or moreguide pins, which are easily visible under the C-arm image generated bythe fluoroscope, can be used to help locate the landmarks, such as thesacral ala and the posterior cortex of the sacral body. Other radiopaquemarkers may be used in place of the pin to help located the position ofthe landmarks. The surgeon may lay the pin against the skin over wherethe underlying osseous landmark is predicted or estimated to be located,and a C-arm image is used to confirm whether the pin is in the correctposition. If the pin(s) are correctly positioned over the landmarks, themark is then drawn on the skin. If the pin(s) are not correctlypositioned, the surgeon may reposition the pin(s) and check pinplacement under fluoroscopy until the pin(s) are correctly positioned.

As illustrated in FIGS. 8A and 8B, the skin marks 700, 702 may be usedas a guide to align the C-arm in the outlet view and the inlet view. Forexample, in some instances, for an outlet view, the C-arm detector 800is positioned over the patient's lower back and oriented perpendicularor normal to the mark 702 identifying the posterior sacral body, and foran inlet view, the C-arm detector 800 is positioned over the patient'slegs and oriented parallel to the mark 702 identifying the anteriorcortex of the sacral body. The C-arm may then be adjusted in both theoutlet and the inlet views until the underlying osseous anatomy isclearly visualized. For example, in the outlet view the C-arm can beadjusted and oriented such that the pubic symphysis and S2 neuralforamina are superimposed on the fluoroscopic image. In someembodiments, the neural foramina of S1, S2, S3 or S4 may be aligned withthe pubic symphysis. In the inlet view the C-arm can be adjusted andoriented such that the sacral prominence of S1 appears as a thin line onthe fluoroscopic image. In addition, in some embodiments, the C-armdetector 800 can be placed under the table (not shown) instead of abovethe patient.

FIGS. 9A and 9B illustrate anatomical features and landmarks of theoutlet view and the inlet view, respectively. The outlet view is ananterior to posterior view of the pelvis and sacrum that provides aclear visualization of the sacral neuro-foramina, such as the S1 foramenand the S2 foramen, as well as other structures such as the inferiorendplate L5 and the superior endplate S1. The inlet view is an anteriorto posterior view of the pelvis that provides a clear visualization ofthe ventral (anterior) cortex of the sacrum. To obtain the inlet view,the C-arm of the fluoroscope is tilted towards the patient's feet untilthe dense cortical line of the S1-S2 vestigial disk directly overliesthe dense cortical line of the sacral promontory. In the inlet view, thesacral canal, the ventral cortex of the sacral body and the sacral alarareas are visualized by the surgeon. Visualization of the osseousanatomy of the sacral ala and the sacral canal allows the surgeon toinsert the implants across the SI-Joint, to keep the leading portion ofthe implants positioned within the sacral ala while avoiding damage tothe neural tissues and vascular structures. In addition, left and rightoblique inlet and outlet views can be obtained to better visualize thesacroiliac joint and surrounding sacral foramina. With the C-arm in theinlet position, an oblique inlet image can be obtained by rotating theC-arm approximately 15 degrees to either side of the patient such thatthe C-arm's beam is approximately parallel to the SI-Joint and thelateral cortical walls of the S1 and S2 foramina. Similarly, with theC-arm in the outlet position, an oblique outlet image can be obtained byrotating the C-arm approximately 15 degrees to either side of thepatient such that the C-arm's beam is approximately parallel to theSI-Joint and the lateral cortical walls of the S1 and S2 foramina.

Implant Placement

Proper implant placement across the SI-joint is determined by thesurgeon selecting and maintaining the correct implant starting position,the correct implant insertion trajectory, and the correct implantlength, which may all be determined with appropriate preoperativeplanning. Preoperative planning includes careful evaluation of osseousanatomy to identify the various landmarks described herein using CTscans and plane radiographs. Safe placement of implants involves placingthe implants across the SI joint keeping the sacral portion of theimplants within the osseous confine of the sacrum while avoiding thenerve tunnels of the spinal canal and neuroforamina, avoidingmalposition of the implant in the dysplastic sacrum, and avoidingin-out-in positioning secondary to the concavity of the ventral surfaceof the sacral ala.

FIGS. 10A and 10B are lateral views that illustrate an embodiment of animplant target zone 1000 that results in the implants passing throughthe articular or hyaline cartilage portion of the SI-joint rather thanthe fibro cartilaginous portion of the SI-joint. The articular cartilageis associated with denser and stronger subchondral bone that can improveimplant stability. Therefore, implants can be implanted into the denserand stronger subchondral bone by passing through the articular boneoutlined by the implant target zone 1000. The location of the articularcartilage is shown as a boomerang or V-shaped outline that is locatedgenerally along the anterior portion of the SI-joint. The implant targetzone 1000 is shown with reference to the various anatomical landmarks inthe lateral view, including the alar line 700, the posterior sacral bodyline 702, and the anterior sacral body line 704. In addition, theanterior portion of the implant target zone 1000 is defined by theanterior cortex of the sacral ala, which is the curved portion of theanterior sacrum that extends from the sacral body to the ilium. In FIGS.10A and 10B, the anterior portion of the implant target zone 1000includes the portion of the implant target zone 1000 that is anteriorthe anterior sacral body line 704. In a lateral view and an inlet view,as illustrated in FIGS. 9C and 9D, the anterior cortex of the sacral alais visible as the most anterior aspects of the sacrum. In the lateralview illustrated in FIG. 9C, the anterior cortex of the sacral ala isdefined generally by the anterior sacral body line 704, the greatersciatic notch, and the superior surface of the sacral ala which formsthe alar line 700. Three implantation sites 1002, 1004, 1006 are shownwithin the implant target zone 1000 in FIG. 10B, with two implantationssites 1004, 1006 located in the anterior portion of the implant targetzone 1000 that corresponds to the anterior cortex of the sacral ala. Theanterior cortex of the sacral ala can serve as a landmark forpositioning those two implantation sites 1004, 1006.

In some embodiments, as shown in FIG. 10C, a first implantation site1002 can be placed with reference to both the alar line 700 and theposterior sacral body line 702. In some embodiments, the firstimplantation site 1002 can be placed with additional reference to theanterior sacral body line 704. For example, in some embodiments thefirst implantation site 1002 can be placed approximately 3 mm to 10 mmfrom the alar line, D1, and approximately 3 mm to 20 mm from theposterior sacral body line 702, D2, where the distance from theposterior sacral body line 702 is measured along a line parallel to thealar line 700. In some embodiments, the first implantation site 1002 canbe placed approximately 5 mm from the alar line 700 and about 10 mm fromthe posterior sacral body line 702. The goal for the first implantationsite 1002 is to place the implant in a superior (cephalad) portion ofthe articular cartilage by using the alar line 700 and the posteriorsacral body line 702 for reference. In some embodiments, the firstimplantation site 1002 can be placed with additional reference to theanterior sacral body line 704, such that the first implantation site1002 is positioned approximately in the midpoint of the posterior andanterior sacral body lines 702, 704. In some embodiments, the firstimplantation site 1002 is positioned anterior of the midpoint of theposterior and anterior sacral body lines 702, 704.

In some embodiments, as shown in FIG. 10D, the second implantation site1004 can be placed with reference to the alar line 700 and the locationof the first implantation site 1002 such that the second implantationsite 1004 is inferior (caudal) and anterior to the first implantationsite 1002 and placed in a middle portion of articular cartilage, nearthe vertex of the boomerang. In some embodiments, the secondimplantation site 1004 can be located anterior of the anterior sacralbody line 704. In some embodiments, the second implantation site 1004can be placed approximately 3 mm to 10 mm from the alar line 700, D3. Insome embodiments, the second implantation site 1004 can be placedapproximately the same distance from the alar line 700 as the firstimplantation site 1002, such that D1 and D3 are approximately equal anda line joining the first implantation site 1002 with the secondimplantation site 1004 is approximately parallel to the alar line 700.In some embodiments, the second implantation site 1004 can be positionedabout 10 mm to about 40 mm from the first implantation site 1002, D4.The distance between the first implantation site 1002 and the secondimplantation site 1004 is generally, at a minimum, at least equal to thediameter of the implant so that the two implants do not overlap. In someembodiments, a guide pin jig can be used to help place the guide pin forthe second implantation site 1004. The guide pin jig can have two holesfor receiving guide pins that are separated by a predetermined distance,D4. In some embodiments, the guide pin jig can have a hole for the firstguide pin and a slot for receiving the second guide pin, so that thedistance between the two guide pins can be varied between about 10 mm toabout 40 mm. In some embodiments, the slot can have distance markingsshowing the distance from the hole for the first guide pin. Moregenerally, the guide pin jig can be used to place the next guide pin byusing the position of a previously placed guide pin.

In some embodiments, as shown in FIG. 10E, the third implantation site1006 can be placed with reference to the anterior sacral body line 704and the second implantation site 1004, so that the third implantationsite 1006 is positioned in an inferior (caudal) portion of the articularcartilage. In some embodiments, the distance between the thirdimplantation site 1006 and the second implantation site 1004, D5, can beapproximately equal to the distance between the first implantation site1002 and the second implantation site 1004, D4. In some embodiments, D5can be between about 0.5 to 2 times the magnitude of D4. In someembodiments, the third implantation site 1006 can be about 0 to 5 mmanterior of the anterior sacral body line 704, D6. In some embodiments,the third implantation site 1006 can be about 2 or 3 mm anterior to theanterior sacral body line 704. As illustrated in FIG. 10E, the threeimplantation sites 1002, 1004, 1006 are located in the anteriorarticular portion of the SI-joint and are non-colinear. If a line isdrawn through the first implantation site 1002 and the thirdimplantation site 1006, the second implantation site 1004 is offset fromthe first and third implantation site by a distance, D7, which can beabout 1 to 15 mm.

The implantation sites described above specify the initial guide pinplacement. In addition to the initial placement, guide pin and implantorientation can be specified to optimize the location of the implantsacross the SI-joint after initial guide pin placement. To orient theguide pins, in addition to the lateral views illustrated in FIGS.10A-10E, the outlet and inlet views described above provide additionallandmarks that facilitate guide pin orientation. Although the followingdescription describes the various guide pins in terms of a first guidepin, a second guide pin, and a third guide pin, the actual order ofinsertion can be varied such that any one of the guide pins can beinserted first, second, or third.

For example, FIGS. 11A-11C illustrate the orientation of the first guidepin 1100 inserted into the first implantation site in the lateral view,the inlet view, and the outlet view. These illustrations and the otherillustrations described herein are illustrative, and variations mayoccur depending on the particular orientations in which the variousviews are taken. As shown in FIG. 11A, the first guide pin 1100 isdriven substantially axially in the lateral view such that the firstguide pin 1100 appears to be driven into the page. In the inlet viewshown in FIG. 11B, the first guide pin 1100 is advanced towards themiddle of the space defined by the anterior sacral line 1104 andposterior sacral line 1102. This target 1106 is illustrated by an X. Insome embodiments, the first guide pin 1100 can be advanced proximate thetarget 1106 since the first guide pin 1100 should not encounter anyneural structures in this orientation, allowing a longer implant to beused for the first implant. In addition, in some embodiments, the firstguide pin 1100 is advanced substantially horizontally in the inlet view.As illustrated in FIG. 11C, in the outlet view the first guide pin 1100is advanced substantially horizontally and is also usually advancedabove the S1 foramen 1108.

FIGS. 12A-12C illustrate the orientation of the second guide pin 1200inserted into the second implantation site in the lateral view, theinlet view, and the outlet view. As shown in FIGS. 12A and 12B, thesecond guide pin 1200 is inserted at an angle α with respect to thehorizontal axis of the inlet view. See also FIGS. 14A and 14B. Todetermine the correct angle of insertion, the distal end of the secondguide pin 1200 is placed or docked at the second implantation site. Thenthe angle of the second guide pin 1200 is set by swinging out theproximal end of the second guide pin 1200 while keeping the distal endfixed until the second guide pin 1200 is pointed towards target 1106illustrated in the inlet view of FIG. 12B, while keeping the secondguide pin 1200 substantially horizontal in the outlet view shown in FIG.12C. In some embodiments, the guide pin 1200 has a trajectory in theinlet view that is centered on the middle third of the body of S1 andaimed towards the target 1106. In general, when the implantation site islocated anterior of the anterior sacral body line 704 in the lateralview, the guide pin is angled by swinging out the proximal end of theguide pin while keeping the distal end fixed until the guide pin ispointed towards target 1106 illustrated in the inlet view. This allowsthe guide pin to follow the anterior surface of the ala and sacrumwithout exiting the anterior surface. In some embodiments, the secondguide pin 1200 is also advanced superior (cephalad) the S1 foramen butinferior (caudal) to the first guide pin in the outlet view. When thesecond guide pin 1200 is advanced superior (cephalad) the S1 foramen1108, it can be possible to advance the second guide pin 1200 all theway to target 1106 as above for the first guide pin. In otherembodiments, the second guide pin 1200 can be advanced horizontallytowards the S1 foramen 1108 in the outlet view, in which case the secondguide pin 1200 is advanced up to but not into the S1 foramen 1108.

FIGS. 13A-13C illustrate the orientation of the third guide pin 1300inserted into the third implantation site in the lateral view, the inletview, and the outlet view. As shown in FIG. 13A, the third guide pin1300 is inserted at an angle in the lateral view, which is expected whenthe implantation site is anterior of the anterior sacral body line 704as shown. As shown in FIG. 13B, the third guide pin 1300 is alsoadvanced towards the target 1106 at an angle β to the horizontal axis.As described above, the angle of the guide pin is set by swinging outthe proximal end of the guide pin while keeping the distal end fixeduntil the guide pin is pointed towards target 1106 illustrated in theinlet view of FIG. 13B, while keeping the guide pin substantiallyhorizontal in the outlet view shown in FIG. 13C. As shown in FIG. 13C,the third guide pin 1300 is advanced substantially horizontally in theoutlet view such that the third guide pin 1300 is directed towards theS1 foramen 1108. In this case, the third guide pin 1300 is advanced upto but not within the S1 foramen 1108. In other embodiments, the thirdguide pin 1300 can be directed between the S1 foramen 1108 and the S2foramen 1110, when the third implantation site is located moreinferiorly (caudally) than illustrated in FIGS. 13A-13C. In this case,the third guide pin 1300 can be advanced past the S1 foramen 1108 andthe S2 foramen 1110 to the medial portion of the sacrum, similar to thefirst guide pin.

FIGS. 14A-14C illustrate the orientation of the three guide pins in thelateral view, the inlet view, and the outlet view. As shown in FIG. 14B,the first guide pin 1100 is inserted horizontally in the inlet view. Thesecond guide pin 1200 is oriented at an angle α with respect to thefirst guide pin 1100 or the horizontal axis in the inlet view. Angle αcan vary depending on the particular implantation site chosen. In someembodiments, angle α can vary between about 0 degrees to about 45degrees, or about 0 degrees to about 30 degrees. The third guide pin1300 is oriented at an angle β with respect to the first guide pin 1100or the horizontal axis in the inlet view. In some embodiments, angle βcan also vary between about 0 degrees to about 45 degrees, or about 0degrees to about 30 degrees. In some embodiments, as shown, the angle βis less than angle α. In other embodiments, angle α is approximatelyequal to angle β. As described in more detail below, implants can beadvanced over the guide pins, resulting in implants having the sameposition and orientation as the guide pins across the SI-joint. Byhaving the implants oriented at an angle with respect to each other andnot parallel to each other, resistance to lateral separation of theSI-joint is increased.

FIGS. 15A-15C illustrate another embodiment of the third guide pin 1300position and orientation when the third implantation site is located inbetween the posterior sacral body line 702 and the anterior sacral bodyline 704 in the inlet view. In this embodiment, the inlet view maydemonstrate that the first and third guide pin are superimposed and theoutlet view may demonstrate that the first and third guide pin aresubstantially parallel. Because the implantation site is located betweenthe posterior sacral body line 702 and the anterior sacral body line704, the third guide pin can 1300 be inserted axially (into the page) inthe lateral view and horizontally in the inlet view shown in FIG. 15B.FIGS. 15A and 15C illustrates the implantation site is located moreinferior (caudal) than shown in FIGS. 13A-13C, and consequently, thethird guide pin 1300 is advanced horizontally between the S1 foramen1108 and the S2 foramen 1110 in the outlet view.

FIGS. 16A and 16B illustrate an assembly 1600 for receiving the guidepin 1602. The assembly can include a soft tissue protector 1604, a drillsleeve 1606 that is removably disposed within the soft tissue protector1604, and a pin sleeve 1608 removably disposed within the drill sleeve1606. The assembly 1600 can be slid over the guide pin 1602 until bonycontact is achieved. FIG. 17 illustrates a pin depth gage 1700 that isplaced against the proximal end of the assembly 1600 so that theproximal end of the guide pin 1602 is aligned with the depth gagemarkings 1702. The pin depth can then be read directly from the markings1702 of the depth gage 1700, allowing the proper implant length to beselected. In some embodiments, the implant is left proud of the ilium'scortical wall by about 2 to 5 mm, so the implant size can be determinedby adding 2 to 5 mm to the pin depth.

Next, as illustrated in FIGS. 18 and 19, the pin sleeve 1608 can beremoved and a drill 1900 with a cannulated drill bit 1902 can beinserted over the guide pin 1602 to prepare a cavity for receiving theimplant. Drilling can be monitored under fluoroscopy in the outlet viewas illustrated in FIG. 20, allowing the user to monitor the depth of thedrill and to watch for unwanted pin advancement. Drilling can be used topenetrate through the entirety of the ilium, to cross the SI joint andto penetrate the lateral cortex of the sacrum. Once the drill 1900 hasreached the appropriate depth, the drill 1900 can be removed with theassistance of an exchange pin 2100, which can be inserted through theproximal end of the drill 1900 and drill bit 1902 until the exchange pin2100 abuts against the guide pin 1602, as illustrated in FIG. 21. Theexchange pin 2100 prevents the guide pin 1602 from withdrawing as thedrill 1900 is removed. When placing the exchange pin 2100 against theguide pin 1602, care should be taken to avoid inadvertently advancingthe guide pin 1602. After the drill 1900 is removed, the drill sleeve1606 can also be removed from the assembly.

For an implant having a rectilinear cross-sectional profile or across-sectional profile defined by a plurality of apices and a pluralityof sides, the soft tissue protector 1604 can have a matchingcross-sectional profile, as shown in FIGS. 22A and 22B. For the firstimplant at the first implantation site, the soft tissue protector 1604can be rotated so that one side of the soft tissue protector is parallelto the alar line 700. In some embodiments, for the second implant at thesecond implantation site, the soft tissue protector 1604 can also berotated so that one side of the soft tissue protector is parallel to thealar line 700. This is appropriate when the second implantation site islocated at the same distance from the alar line 700 as the firstimplantation site, as described above. Such a configuration allows theimplant 2200 to be positioned close to the alar line without penetratingthrough the cortices. For the third implant, the soft tissue protectorcan be rotated so that one side of the soft tissue protector 1604 isfacing the greater sciatic notch 2202. FIG. 22C illustrates theorientation of the faces of the implants 2200 to the anatomicallandmarks in the lateral view.

FIG. 23 illustrates an embodiment of a broach 2300 and a mallet 2302that can be used to create a rectilinear bore to match the shape of theimplant. The broach 2300 has a distal end having a plurality of cuttingedges and surfaces for removing bone. The mallet 2302 can have a slot2306 in the mallet head 204 for receiving an exchange pin 2100 thatallows the mallet 2302 to be used in conjunction with the exchange pin2100. The broach 2300 can be inserted over the guide pin 1602 and intothe soft tissue protector 1604 until it contacts the bone. Asillustrated in FIG. 24, the broach 2300 can be tapped with the mallet2302 across the SI-joint under visualization in the outlet view. Thebroach 2300 can be removed with the exchange pin 2100 in place in orderto prevent the guide pin 1602 from withdrawing as the broach 2300 isremoved.

After the broach 2300 has been removed, the implant 2200 can be placedover the guide pin 1602 and an impactor 2500 can be used to advance theimplant 2200 into the broached bore, as illustrated in FIGS. 25A and25B. The alignment of the soft tissue protector 1604 can be checked andadjusted as needed so that one side of the soft tissue protector isaligned with the alar line 700. In some embodiments, autograft orallograft bone derived materials, for example the bone materialsgenerated by the drill and broach, can be applied to the implant surfacebefore insertion. Other materials for coating the implant 2200 includegrowth factors such as bone morphogenetic protein. In some embodiments,the implant 2200 can have a tapered distal end 2202 that is insertedinto the bore first. FIG. 26 illustrates a slotted mallet 2302, asdescribed above, being used to strike and advance the impactor 2500 andimplant 2200. The slot 2306 in the mallet 2302 can receive an exchangepin 2100 and allows the mallet 2302 to be used in conjunction with anexchange pin 2100, if desired. As illustrated in FIGS. 27A and 27B,implant advancement can be monitored under fluoroscopy in the outletview to ensure that the implant avoids the foramen. The implant 2200 isadvanced until about 2 to 5 mm of the implant remains proud of thesurface of the ilium, as shown in FIG. 28.

SI-Joint Implants

Various implants 2200 can be used for the fixation and fusion of theSI-Joint, as illustrated in FIGS. 29A and 29B. These include screw likeimplants that are threaded or unthreaded implants or implants with boththreaded and unthreaded portions. In some embodiments, the unthreadedimplants can have a rectilinear cross-sectional profile transverse tothe longitudinal axis of the implant, such as triangular or rectangular.In other embodiments, the unthreaded implants can have a cross-sectionalprofile defined by one or more apices joined by one or more sides whichcan be either rectilinear or curvilinear. Implants with a rectilinearcross-sectional profile or a cross-sectional profile defined by one ormore apices can better resist rotation than a screw like implant with acircular cross-sectional profile.

Use of a round implant such as a screw type implant may requiremodifications to portions of the procedure described above including,for example, replacing the soft tissue protector with a standard tubulardilator system, and elimination of the broach and impactor.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions are incorporated herein byreference in their entirety. For example, features described in oneembodiment may be combined with another embodiment. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

What is claimed is:
 1. A method of implanting a plurality of implantsacross an SI-joint, the method comprising: identifying a plurality ofanatomical landmarks in the lateral view including the alar line, theposterior sacral body line, the anterior sacral body line, and theanterior cortex of the sacral alar; inserting a plurality of guide pinsacross an anterior portion of the SI-joint and through hyalinecartilage, wherein the plurality of guide pins are inserted withreference to at least one anatomical landmark; creating a bore aroundeach of the plurality of guide pins; and inserting an implant into eachbore such that each implant crosses the anterior portion of the SI-jointand passes through hyaline cartilage, wherein at least one guide pin andimplant are inserted anterior of the anterior sacral body line in thelateral view.
 2. The method of claim 1, wherein at least two guide pinsand implants are inserted anterior of the anterior sacral body line inthe lateral view.
 3. The method of claim 1, wherein the at least oneguide pin and implant that is inserted anterior of the anterior sacralbody line in the lateral view is angled with respect to a horizontalaxis in an inlet view.
 4. The method of claim 1, wherein at least twoguide pins and two implants are placed parallel to the alar line.
 5. Themethod of claim 1, wherein the plurality of guide pins are parallel inan outlet view.
 6. The method of claim 1, further comprising identifyinga target for the plurality of guide pins in an inlet view, wherein thetarget is located in the middle of the sacral body.
 7. The method ofclaim 6, further comprising advancing the guide pins towards the targetin an inlet view.
 8. The method of claim 1, wherein the implants arenon-colinear in the lateral view.
 9. The method of claim 1, wherein theimplants have an elongate body with a longitudinal axis and arectilinear cross-sectional profile transverse to the longitudinal axis.10. The method of claim 1, wherein the implants are screws.